U.S. patent number 6,569,336 [Application Number 09/959,960] was granted by the patent office on 2003-05-27 for method, device and use of said method for biological elimination of metal elements present in an ionized state in water.
This patent grant is currently assigned to Degremont. Invention is credited to Joan-Yves Bergel, Pierre C. Mouchet.
United States Patent |
6,569,336 |
Mouchet , et al. |
May 27, 2003 |
Method, device and use of said method for biological elimination of
metal elements present in an ionized state in water
Abstract
The method, in which the water to be treated is partly
oxygenated by a specific aeration carried out before percolation
through a biofilter having a bacteria-supporting bed of filtering
material, has a measurement stage of at least one parameter
constituted by the oxidation-reduction potential of the aerated
water before passage into the biofilter, a transmission stage of
measurement signals to a computer and comparison of the signal
representative of the value of the measured parameter with at least
one lower limit set in function of the measurement carried out in a
second stage for measuring a parameter representative of the pH and
a stage for correcting the air flow by a signal determined by the
computer in function of the two preceding stages.
Inventors: |
Mouchet; Pierre C. (Rueil
Malmaison, FR), Bergel; Joan-Yves (Ville Saint
Laurent, CA) |
Assignee: |
Degremont (Rueil Malmaison,
FR)
|
Family
ID: |
9545523 |
Appl.
No.: |
09/959,960 |
Filed: |
January 31, 2002 |
PCT
Filed: |
April 28, 2000 |
PCT No.: |
PCT/FR00/01139 |
PCT
Pub. No.: |
WO00/69779 |
PCT
Pub. Date: |
November 23, 2000 |
Foreign Application Priority Data
|
|
|
|
|
May 12, 1999 [FR] |
|
|
99 06058 |
|
Current U.S.
Class: |
210/614; 210/220;
210/743; 210/620; 210/746 |
Current CPC
Class: |
C02F
3/346 (20130101); C02F 3/04 (20130101); G05D
21/02 (20130101); C02F 3/006 (20130101); C02F
2101/20 (20130101); C02F 2103/06 (20130101); C02F
2209/06 (20130101); C02F 2209/07 (20130101); C02F
2209/04 (20130101); C02F 2209/225 (20130101); C02F
1/66 (20130101); Y02W 10/15 (20150501); Y02W
10/10 (20150501) |
Current International
Class: |
C02F
3/00 (20060101); C02F 3/34 (20060101); C02F
3/04 (20060101); G05D 21/00 (20060101); G05D
21/02 (20060101); C02F 1/66 (20060101); C02F
003/00 () |
Field of
Search: |
;210/746,743,620,220,614 |
Foreign Patent Documents
|
|
|
|
|
|
|
1767738 |
|
Mar 1971 |
|
DE |
|
17 67 738 |
|
Mar 1971 |
|
DE |
|
4111375 |
|
Oct 1992 |
|
DE |
|
41 11 375 |
|
Oct 1992 |
|
DE |
|
42 31 363 |
|
Mar 1994 |
|
DE |
|
4231363 |
|
Mar 1994 |
|
DE |
|
196 40 899 |
|
Jan 1998 |
|
DE |
|
19640899 |
|
Jan 1998 |
|
DE |
|
0 695 720 |
|
Feb 1996 |
|
EP |
|
0 695 720 |
|
Feb 1996 |
|
EP |
|
2 470 094 |
|
May 1981 |
|
FR |
|
2470094 |
|
May 1981 |
|
FR |
|
Other References
Copy of US trademark registration application information for
registration application Ser. 73/661833 (dead), (DEGREMONT SA,
applicant), showing BIOLITE (design mark plus words, at
http://tess.uspto.gov/bin/showfield?f=doc&state=p808h.2.11..
|
Primary Examiner: Barry; Chester T.
Attorney, Agent or Firm: Nixon & Vanderhye
Claims
What is claimed is:
1. Method for elimination by biological route of metallic elements
present in the ionized state in water devoid of dissolved oxygen,
in which the water to be treated is partially oxygenated by a
specific aeration carried out before percolation through a
biofilter reactor with a bacteria-supporting bed of filtering
material, characterised in that it comprises: a measurement stage
for at least one parameter constituted by the oxidation-reduction
potential (Eh) of the aerated water before passage into the
biofilter; a transmission stage of measurement signals to a
computer and comparison with the signal representative of the value
of at least one parameter measured for at least one lower limit of
this parameter determined in function of the measurement carried
out in a second stage of measurement of a second parameter
representative of the pH and a possible stage for correction of the
air flow by control by a unit (3, 10, 11) for adjusting the air
flow by a signal determined by the computer in function of the two
preceding stages.
2. Method according to claim 1, characterised in that it further
comprises a stage for measuring the second parameter constituted by
the pH of the aerated water before passage into the biofilter, and
a stage of comparison with a lower and upper limit of the first
parameter whose lower and upper limits are determined in function
of the measurement of the second parameter.
3. Method according to claim 1, characterised in that it comprises
a stage for compensation of a fault in the adjustment of the air
flow by the first parameter by means of a system of complementary
regulation using at least one signal provided by measurement means
(12) of the residual content of oxygen dissolved in the treated
water.
4. Method according to claim 1, characterised in that the
compensation stage uses a second signal provided by measurement
(13) of the pH of the treated water simultaneously with that of the
dissolved oxygen.
5. Method according to claim 2, characterised in that it comprises
an adjustment stage of the pH of the filtered water through
injection of an alkaline solution (19) into the water to be
treated, if the signal provided by the measurement means (13) of
the pH representative of the pH value of the treated water is lower
than an assigned lower value, said injection being limited by an
assigned set upper value for the pH.
6. Method according to claim 1, characterised in that it comprises
a stage for verifying the efficiency of the treatment by continuous
measurement of the content of residual dissolved iron and the
oxidation-reduction potential of the filtered water, with an alarm
being set off in the event of anomaly.
7. Utilisation of the method according to claim 2, characterised in
that the method is used in a biofilter with a ferro-bacteria
supporting bed of filtering material.
8. Utilisation of the method according to claim 1, characterised in
that the method is used in a biofilter with a mangano-bacteria
supporting bed of filtering material.
9. Utilisation of the method according to claim 1, characterised in
that the method is used in a biofilter with an
autotrophic--bacteria supporting bed of filtering material.
10. Utilisation of the method according to claim 2, characterised
in that the method is used in a first biofilter with a
ferro-bacteria supporting bed of filtering material, and then the
treated water exiting from this first biofilter is used according
to the method of claim 1 in a second biofilter with a
mangano-bacteria supporting bed of filtering material.
11. Device for treating waters devoid of dissolved oxygen,
characterised in that it comprises an aeration chamber (4) into
which the raw water and injected air are brought, the flow of the
latter being controlled by a valve (3) allowing controlled aeration
under pressure, and whose exit is linked to a biofilter reactor
provided with an outlet (7), and with a porous ferro-bacteria
supporting bed through which the water to be treated percolates,
first measurement means (8) of the pH and second measurement means
(9) of the oxidation-reduction potential (Eh) of the aerated water,
set between the aeration chamber and the filter, the calculating
units (10) taking into account the signals delivered by the first
and second measurement means to send a command signal to a means
for regulation of the air flow (11, 16) acting on the valve (3) to
allow regulation in function of a lower limit and an upper limit
for the potential Eh, determined for a given pH value.
12. Device according to claim 11, characterised in that it
comprises means (13) for measuring the pH and means (12) for
measuring the dissolved oxygen at the outlet from the filter (5)
and units for computing (14) and regulating (16) the air flow to
allow complementary adjustment of the method.
13. Device according to claim 11, characterised in that it
comprises a station for regulating the pH comprising a reservoir
(20) of an alkaline solution (19) controlled by an electro-valve or
feed pump which is monitored by the signal worked out by a
regulation unit (17) and allowing the adjustment of the pH in
function of the signal delivered by the measurement means (13) of
the pH set at the outlet from the biofilter reactor to the
regulation unit (17).
14. Device according to claim 11, characterised in that it
comprises means (21, 22) for measuring the oxidation-reduction
potential of the residual iron in the filtered water, set at the
outlet from the filter and allowing evaluation of the efficiency of
the device.
15. Device for treating waters devoid of dissolved oxygen according
to claim 11, characterised in that the outlet from the
ferro-bacteria biofilter reactor is linked to a second aeration
chamber (4') into which is brought the water treated ny the
ferro-bacteria biofilter reactor and air injected by a second valve
(3'), the exit from the aeration chamber (4') being linked to a
second biofilter reactor (5') provided with an outlet (7') and
having a porous mangano-bacteria supporting bed through which the
treated water from the ferro-bacteria biofilter percolates and
third measurement means (9') of the oxidation-reduction potential
(Eh) at the exit from the second aeration chamber, a calculation
unit (10') taking into account the signal delivered by the third
measurement means to send a command signal to a regulation means
(11') acting on the second valve (3') to allow adjustment of the
air flow in function of a given lower limit.
16. Device according to claim 11, characterised in that the
filtering bed is constituted of siliceous sand of an effective size
comprised between 1 and 3 mm.
17. Device according to claim 11, characterised in that the
filtering bed is constituted of a filtering material, called
"Biolite".
Description
The present invention relates to a method for optimizing and
monitoring automatically, by biochemical route, the elimination
parameters of metallic elements present in the ionized state in
water, for example ground or surface waters, the device for
implementing said method and use of said method.
More particularly, the invention concerns a method and a device for
elimination by biological route of divalent elements, such as
divalent iron and manganese, present in groundwater.
The invention can be extended to surface waters devoid of dissolved
oxygen where these elements are present in the same state, such as
the reducing hypolimnion water above a dam in a state of
eutrophication.
The oxidation of minerals by biological route has already been the
object of in-depth studies and practical applications. This family
of methods uses the capacity of certain specific bacterial strains,
indigenous and/or incorporated, to catalyse by the exothermic
oxidation reactions by enzymatic conversion. In return, these
exothermic oxidation reactions provide the bacteria with the energy
necessary for their development. This family of methods has been
applied in particular in the mining industry for many years.:
either in the domain of extractive hydrometallurgy, whose first
phases consist of pulverisation of the ore, enrichment by flotation
and leaching in an acid or alkaline medium; biological leaching, or
"bioleaching", often in competition now with purely chemical
leaching. The most widespread applications have concerned, until
recent years, the copper industry (see the work by N. N. Hughes
& R. K. Poole: "Metals & Micro-organisms", published by
Chapman & Hall, 1989, and the article by D. Morin:
"Biotechnologies dans la metallurgie extractive", published in Les
Techniques de l'Ingenieur, Paris 1995, No. M2238, vol. 1): the ore,
more or less fractionated, is simply heaped in the open air and
sprinkled with a solution of nutritive elements. This method, known
under the name of "heap leaching", does not require any precise
monitoring during the operation; or for the treatment of acid
effluents containing high amounts of dissolved divalent iron. The
Japanese patent No. 44717/72 describes a method in which the
culture of iron bacteria was carried out in a treated effluent, and
then tipped into the effluent to be treated. In the Japanese patent
No. 38 981/72, the method was improved by producing the bacterial
culture `in situ`, on supports constituted of iron oxides. A
further improvement was provided by the French patent No.
2.362.793, filed in 1976, where the bacterial culture was fixed on
an insoluble support, at the pH of the effluent, and where the
ferrous irons (Fe.sup.2+) were oxidised by air blowing into an
agitated reactor. The bacteria and their supports were then
separated by decanting, then recycled in the reactor, as in a
system for treating urban waste water by the activated sludge
method. In such cases as well, control of the process does not pose
any problem. In particular, the low pH level of the medium avoids
any competition between the physico-chemical route and the
biological route for iron oxidation, which in practice means
absence of the need for monitoring the quantity of oxygen
introduced and the quantity of residual oxygen in the water after
treatment.
Later, it was considered that these phenomena could be applied to
the elimination, by biological route, of the iron and manganese
present in the dissolved state in natural water deprived of oxygen
and whose pH value, contrary to the effluents mentioned above, is
situated close to neutrality, roughly plus or minus one unit. In
this field, even if it concerns species different from those
characteristic of acid effluents, it was already known that
bacteria capable of catalysing iron and/or manganese oxidation,
still called ferro- and mangano-bacteria, could, thanks to
exogenous enzymes and/or polymers, by detected in very diverse
environments (groundwater, lake beds, emergent springs in marine
bays, etc . . . ). The damage from ferro- or mangano-bacteria
clogging up well drains or corroding metallic piping was already
well known, these bacteria needed to be "domesticated" to make them
work usefully in plants for eliminating dissolved iron and
manganese.
The first observations on this subject were published by U.
Hasselbarth & D. Ludemann (in the article "Die Biologische
Enteisenung und Entmanganung", Vom Wasser, 1971, vol. 38, pp.
233-253; "Removal of iron and manganese from groundwater by
microorganisms", Water Treatment & Examination, 1973, vol. 22,
No. 1, pp. 62-77 and were concretised by the same authors filing
the German patent No. 1.767.738. This patent describes a method for
biological iron removal by oxygenation and filtration, under
conditions such that the power of oxidation-reduction of the medium
has a value rH higher than or equal to 14.5.+-.0.5. The rH is an
index analogous to the pH, representing quantitatively the value of
the oxidising or reducing power of a medium. This rH value
corresponds to the lower limit of the domain of action of
ferro-bacteria. Thus a minimum condition was defined, but it only
represented a threshold, moreover insufficient, for total iron
removal and it did not make it possible to define the lower and
upper limits on which to base the automatic regulation of the
method.
Besides, the authors defined very limited and very restrictive
oxygenation conditions for the method, probably because they did
not have a variety of types of untreated water available. The
development of this promising method was thus delayed.
At about the same time, similar studies were undertaken in France
(P. Mouchet & J. Magnin: "Un cas complexe de deferrisation
d'une eau souterraine", TSM-l'eau, 1979, vol. 74, No. 3, pp.
135-143), but for very differing waters, which made it possible for
the French researchers to define more precisely the limits for
biological iron removal and to provide, at the 1985 "Wasser Berlin"
Congress, the construction of about thirty installations based on
this principle of biological treatment (see the article of P.
Mouchet et al. entitled "Elimination of iron and manganese
contained in groundwater: classic problems, recent progress",
published in Water Supply, 1985, vol. 3, No. 1, pp. 137-149).
Besides, at the same time, the German researchers had noted that
many plants could operate spontaneously on this principle (see the
article by C. CZEKALLA et al. entitled "Quantitative removal of
iron and manganese by microorganisms in rapid sand filters (in situ
investigations)", published in Water Supply, 1985, vol. 3, No. 1,
pp. 111-123). Moreover, similar observations had stimulated French
research at the beginning of the seventies.
Thus from reading the above, one can note that biological iron
removal was the method studied the most and the best known at the
beginning of this research, probably because the natural seeding by
indigenous bacteria is relatively rapid. On the contrary, the
seeding time concerning biological manganese removal, a matter of
several weeks, or even two or three months, did not encourage
studies on manganese removal, at least to begin with.
The results of French research, published in 1985, described among
others the field of activity of ferro-bacteria, such as shown in
FIG. 4, within which, moreover, the domain of existence of a
treatment ensuring total iron elimination is submitted to more
restrictive limits.
Such a diagram, drawn with ordinate the oxidation reduction
potential and with abscissa the pH, is called a stability diagram.
It was drawn up first by M. J. POURBAIX to study corrosion
phenomena of ferrous metals, and was later extended to the
speciation of the principal elements (see the works of M. J.
Pourbaix entitled "Atlas d'equilibres electrochimiques a 25.degree.
C.", published by Gauthier-Villars, Paris 1963, pp 307-321) and
applied to the study of iron removal from groundwater (see article
by J. D. Hem, entitled "Stability field diagrams as aids in iron
chemistry studies", published in the AWWA Journal, 1961, Vol. 53,
No. 2, pp. 211-232).
The domain of biological iron removal (Db) or ferro-bacterial
activity is defined by a minimum rH value and a maximum rH value,
the zone comprised below the curve (rHmin) representing the minimum
rH value corresponding to the stability domain (DFe.sup.2+) of the
ferrous ion and the zone comprised above the curve (rHmax)
representing the maximum rH corresponding to the domain (Dpc) of
physico-chemical iron removal. The optimum domain for biological
iron removal (Db) overlaps the theoretical limit (DFe.sup.2+
/Fe.sup.3+) separating the respective domains of the ferrous iron
and the ferric hydroxide.
The diagram in FIG. 4 shows that biological iron removal from
natural water, whose pH can vary from values lower than 6 up to
values higher than 8, can only be produced under certain conditions
of oxidation-reduction potential and pH for which there is
enzymatic oxidation of the ferrous ions Fe.sup.2+ without
precipitation of basic salts of ferric iron Fe.sup.3+, that is
without production of physico-chemical iron removal whose
performances are much more modest than those of biological iron
removal.
In the water before treatment, the oxidation-reduction potential
(or Eh) varies in function of the concentration of oxygen dissolved
brought by aeration, whereas in treated water the Eh depends more
on the value of the Fe.sup.3+ /Fe.sup.2+ couple, that is to say the
degree of iron oxidation. In FIG. 4, it can be clearly seen that
the oxidation conditions must be more closely monitored as the pH
rises. In particular, when the pH is greater than 7.6 in untreated
water, the level of oxygen dissolved must be lower than a maximum
threshold, very limited, the exact upper limit being lowered as the
pH rises. This pH value is comprised between 7.6 and 8.5 defining a
domain (Dbc) where the iron removal is difficult to adjust because
of the competition between the biological oxidation and the
physico-chemical oxidation.
Since a level of oxygen dissolved at a concentration higher than
50% of saturation point is nonetheless desirable in treated water,
in particular to avoid fermentation and corrosion during
distribution, these observations have led to the concept of
biological iron removal plants, for all waters at pH>7,
following the diagram of FIG. 5. In this design, untreated water
undergoes a first aeration carried out in a mixer 31, specially
studied to obtain an immediate mixture of air and water. The water
is then submitted to biological iron removal by high-speed
percolation through a bed of specific filtering material, a
ferro-bacteria support in a biofilter reactor 32 studied specially
for this. The filtered water is then submitted to a final intensive
aeration in a new mixer 33. The filter bed is made of a material
marketed under the brand name Biolite.RTM..
The necessity for perfect control of the quantity of oxygen
injected for all waters with pH>7.3 led to the French patent No.
2. 470.094, filed in 1979 by the Applicant. This patent describes
an invention according to which the oxygen was introduced into the
water to be treated by recycling part of the treated water. This
treated water was previously brought close to saturation in
dissolved oxygen through a final intensive aeration, the quantity
of oxygenated recycled water being a function of the pH of the
water to be treated and its oxygen requirements, and adjusted using
a rotameter or other apparatus for measuring flow.
Continuing research in France then made it possible to set the
limits of the domain for biological manganese removal and to
compare them with those of biological iron removal. FIG. 6 shows
that the two domains are separate and that there is no common point
between the zone (A) of the biological route for iron removal,
overlapping the theoretical limit (DFe.sup.2+ /Fe.sup.3+)
separating the respective domains of the ferrous ion and ferric
hydroxide, and zone (B) of the biological route for manganese
removal overlapping the theoretical limit (DMn.sup.2+ /Mn.sup.4+)
separating the respective domains of the Mn.sup.2+ ion and
manganese dioxide (MnO.sub.2).
The result is that for water containing the two elements together,
the solution generally adopted is treatment in two filtration
stages, described in the article by P. Mouchet "From conventional
to biological removal of iron and manganese in France", published
in the Journal AWWA, 1992, vol. 84, No. 4, pp. 158-167, a first for
iron removal and a second for manganese removal, each stage
specifically receiving its own adjustments of oxygen injection and,
if required, adjustment of the pH.
This know-how represents the prior state of the art, before the
present invention, from which it is clear that for correct running
of a treatment plant for iron removal and, if necessary, manganese
removal by biological route, the surrounding conditions in the
treatment medium must be adjusted continually, in order to avoid
any inhibition of bacterial activity. These conditions depend on a
certain number of parameters, such as the pH, the
oxidation-reduction potential, the temperature, the substrate
concentrations, the element to be oxidised, and oxygen.
Any fault in adjustment or operation of the oxygen-supply and/or pH
correction devices leads to malfunction of the treatment unit,
resulting in a lowering of the oxidation efficiency of the element
to be oxidised. Nonetheless, biological elimination has many
advantages over conventional physico-chemical treatment: higher
quality of treated water, compactness of treatment plants, higher
treatment speed, absence of reactive agents (flocculants,
oxidants), loss of charges reduced, significant reduction of
investment and running costs, better production yields of
dehydration of sludge, enough significant advantages to be a real
incentive to overcome the defects and malfunctions mentioned
above.
In the domain of biological iron removal, said defects and
malfunctions can arise from: either a lack of oxygen, which would
limit the respiration needs of the biomass, and would situate the
water at a level of low oxidation-reduction potential; or an excess
of oxygen, which would situate the water at a level of too high
oxidation-reduction potential, and would inhibit microbe activity.
These conditions could even create competition between
physico-chemical oxidation and bacterial activity; or too low an
acid pH (less than 6 to 6.5) which would situate the water under
the minimum threshold for oxidation-reduction potential (Eh),
required for micro-organisms to react to provide total oxidation of
the element to be eliminated; or, finally, too high a basic pH
(over 7.8 to 8) which would situate the water above the maximum
threshold for oxidation-reduction potential, encouraging
competition between chemical oxidation of the element to be
oxidised and bacterial activity, even going as far as inhibiting
this bacterial activity.
On the other hand, biological manganese removal is less sensitive
to the medium parameters, although it is nevertheless useful to
ensure permanently that, before entering the manganese removal
reactor, the water to be treated has a sufficiently high pH
(greater than about 7.2) and a content of dissolved oxygen greater
than 50-60% saturation to be in the domain (B) defined in FIG. 6.
The control of these biological treatments therefore rests on that
of the operational physico-chemical parameters, which is not easy
for small plants and when the oxygen content (O.sub.2) dissolved
has to be very low for the process (sometimes less than 1.0 mg/l
for biological iron removal from waters with pH higher than 7.5).
The present invention solves this type of problem by providing a
method for regulating the process in function of the
characteristics of the raw water.
It can be noted that a similar philosophy for biological processes
has also appeared in other domains, for example: for anaerobic
treatment of waste water (see patent FR 2 672 583 or U.S. Pat. No.
5,248,423, filed by the Applicant in 1992). for extractive
hydrometallurgy , for biofiltration of metals more rare and more
precious than copper, for example gold, (see the article by A.
Kontopoulos & M. Stefanakis, "Process options for refractory
sulfide gold ores: technical, environmental and economical
aspects", 1991, 393; the article by J. Libaude, "Le traitement des
minerais d'or" published in Recherche, May 1994) or cobalt (see the
article by D. Morin et al. "Study of the bioleaching of a
cobaltiferrous pyritic concentrate", published in IBS proceedings,
1993, vol. 1, p. 147; the article by D. Morin "Des bacteries vont
extraire le cobalt", published in Recherche, 1998, No. 312, pp.
38-40). It should be noted that the gangue, from which these metals
are extracted, is often constituted mainly of pyrite, which here
again implies a major action of ferro-bacteria adapted to acid
media, already mentioned above relative to the treatment of acid
effluents from mines.
Nonetheless, the invention described here has no point in common
with the above domains, where for example the composition of
methane-containing gas intervenes, on the flow of raw water under
anaerobic treatment of effluent, or a process for bioleaching is
controlled by reactor hydraulics, the introduction of adapted
bacterial strains and/or the adjustment of the temperature.
In the present case, the conditions of oxidation of raw water will
primarily be adjusted automatically as a function of the
characteristics of the raw water, the aerated water before
treatment and/or the final treated water. A first approach to this
type of regulation was tried out on the bases of the Eh potential
of the water treated (see the article by C. Tremblay et al.,
"Control of biological iron removal from drinking water using ORP",
published in IAWO, Vancouver, 1998, June) similar to other devices
studied for treating waste water (see the article by J. Charpentier
et al, "Oxidation-reduction potential (ORP) regulation: A way to
optimize pollution removal and energy savings in the low load
activated sludge process", published in Water Sci. Tech., 1987,
vol. 19, No. 3-4, pp. 645-656; and the article by D. G. Warcham et
al, "Real-time control of wastewater treatment systems using ORP",
published in Wat. Sci. Tech., 1993, vol. 28, No. 11-12, pp.
273-282). The tests based on this principle, carried out by the
Applicant, resulted in failure.
In fact, in treated waste water, the final oxidisation-reduction
potential Eh takes into account the transformation of carbonaceous,
nitrogenous, phosphorated, sulphurated etc. species, of which only
a fraction can be eliminated from the water by stripping or
stocking in bacteria: a fraction of these compounds therefore
remains dissolved, under a partly reduced/partly oxidised form, and
the final potential depends on the respective proportions of the
two forms of the oxidation-reduction system.
On the other hand, as far as iron and manganese removal are
concerned, the reduced forms of the metals are oxidised and
precipitated, thus quasi-eliminated from the dissolved matrix. For
a given pH, the final oxidation-reduction potential Eh is
representative of this elimination, whether it takes place by
physico-chemical or biological route. Furthermore, it is
independent of the content of dissolved oxygen, since the normal
potential of the O.sub.2 /H.sub.2 O couple is very much lower than
that of the Fe.sup.3 +/Fe.sup.2 + couple. Measurement of the Eh of
treated water thus has a certain interest as a parameter indicative
of the efficiency of the treatment, which has moreover been
demonstrated by the authors quoted above, who were able to
establish a significant relationship between this value and the
residual iron content in the filtered water. On the other hand, in
no case can this measurement serve as a basis for regulating the
process.
The aim of the present invention is to propose a process making it
possible to avoid such risks and to regulate a treatment for
biological elimination of elements present under ionized form.
This aim can be attained through the fact that the elimination
process, by biological route, for metallic elements present in the
ionized state in waters devoid of dissolved oxygen, in which the
water to be treated is partially oxidised by a specific aeration
carried out before percolation through a biofilter reactor
including a bacteria-supporting bed of filtering material, is
characterised in that it comprises: a measurement stage for at
least one parameter constituted by the oxidation-reduction
potential (Eh) of the aerated water before passage into the
biofilter; a transmission stage of measurement signals to a
computer and comparison with the signal representative of the value
of at least one parameter measured for at least one lower limit of
this parameter determined in function of the measurement carried
out in a second stage of measurement of a second parameter
representative of the pH and a possible stage of correction of the
air flow by control by a unit for adjusting the air flow by a
signal determined by the computer in function of the two preceding
stages.
According to another characteristic, the process comprises a stage
for measuring the second parameter constituted by the pH of the
aerated water before passing into the biofilter, a stage of
comparison with a lower and higher limit of the first parameter
whose lower and higher limits are determined in function of the
measurement of the second parameter.
According to another characteristic, the process comprises a stage
for compensation of a fault in the regulation of the air flow by
the first parameter by means of a system of complementary
regulation using at least one signal provided by a means of
measurement of the residual content of oxygen dissolved in the
treated water.
According to another characteristic, the compensation stage uses a
second signal provided by means of measurement of the pH of the
treated water simultaneously with measurement of the dissolved
oxygen.
According to another particularity, the process comprises a stage
for regulation of the pH of the filtered water by injection of an
alkaline solution into the water to be treated; if the signal
provided by means of the measurement of the pH and representative
of the value of the pH of the water treated is lower than a fixed
lower value, said injection being limited by a fixed higher set
value of the pH.
According to another particularity, the process comprises a stage
for verification of the efficiency of the treatment by continuous
measurement of the residual dissolved iron content and
oxidation-reduction potential of the filtered water, with an alarm
being set off in the event of an anomaly.
Another aim of the invention is to propose a device for elimination
of elements present under ionized form in ground water or surface
water.
This aim is attained by the fact that the device for the treatment
of water devoid of dissolved oxygen according to the invention is
characterised in that it comprises an aeration chamber into which
the raw water and injected air are introduced, whose flow is
adjusted by a valve allowing controlled aeration under pressure and
whose outlet is linked to a biofilter reactor, provided with an
exit, with a porous ferro-bacteria supporting bed through which the
water to be treated percolates, first pH measurement means and
second oxidation-reduction potential measurement means of the
aerated water, set between the entrance chamber and the filter,
calculating units taking into account the signals delivered by the
first and second measurement means to deliver a command signal to a
means for adjusting the air flow acting on the valve to enable
regulation in function of an upper and lower limit of Eh potential,
determined for a given pH value.
According to another characteristic, the device comprises pH
measurement means and means for measuring the dissolved oxygen at
the exit from the filter and units for calculating and regulating
the air flow to allow complementary regulation of the process.
According to another characteristic, the device comprises a pH
regulation station comprising a reservoir of alkaline solution
controlled by an electro-valve or a feed pump which is monitored by
the signal worked out by a regulation unit and allowing regulation
of the pH in function of the signal delivered by the pH measurement
means set at the exit from the biofilter reactor to the regulation
unit.
According to another particularity, the device comprises means for
measuring the oxidation-reduction potential of residual iron in the
filtered water, set at the exit from the filter and enabling
evaluation of the efficiency of the device.
According to another particularity, the exit from the biofilter
reactor with ferro-bacteria is linked to the entry of a second
aeration chamber in which the treated water is sent from the
biofilter reactor with ferro-bacteria and air injected by a second
valve, the exit from the aeration chamber being linked to a second
biofilter reactor provided with an exit and lined with a porous
mangano-bacteria supporting bed through which the treated water
coming from the ferro-bacteria biofilter filters and third
measurement means of oxidation-reduction potential at the exit from
the second aeration chamber, a computing unit taking into account
the signal delivered by the third measurement means to deliver a
command signal to a means of regulation acting on the second valve
to allow regulation of the air flow in function of a given lower
limit.
According to another characteristic, the filter bed is constituted
of siliceous sand of effective size between 1 and 3 mm.
According to another characteristic, the filter bed is constituted
of a filtering material, called "Biolite", specially designed for
this type of treatment.
Another aim of the invention is to propose a utilisation for said
process.
This aim is attained in that the process is used in a biofilter
with a ferro-bacteria supporting bed of filtering material.
According to another characteristic, the process is used in a
biofilter with a mangano-bacteria supporting bed of filtering
material.
According to another characteristic, the process is used in a
biofilter with an autotrophic bacteria supporting bed of filtering
material.
According to another characteristic, the process is used in a first
biofilter with a ferro-bacteria supporting bed of filtering
material, and then the treated water exiting from this first
biofilter is used in a second biofilter with a mangano-bacteria
supporting bed of filtering material.
Other characteristics and advantages of the present invention will
become clear by reading the description below referring to the
attached drawings in which:
FIG. 1 shows a diagram of a device, according to the invention, for
iron removal from ground water;
FIG. 2 shows an iron removal and manganese removal device for water
according to the invention;
FIG. 3 shows the results of biological iron removal according to
the invention compared with those obtained according to
physico-chemical iron removal;
FIG. 4 shows a stability diagram of prior art illustrating the
domain of activity of ferro-bacteria;
FIG. 5 shows a device for biological iron removal of prior art;
FIG. 6 shows the biological iron removal and manganese removal
domains defined by prior art.
The invention will now be described with reference to the
figures.
The process consists of measuring the following parameters: the pH
and oxidation-reduction potential, on previously aerated water, and
possibly the pH and/or dissolved oxygen on the water treated by the
biomass. From these measurements and in real time the monitoring
unit acts on different adjustment mechanisms in order to adjust the
operational conditions best adapted to the correct operation of the
ecosystem in the reactor where the biological reaction takes place
with the biomass. These control units are such as indicated in FIG.
1, which is only one embodiment of a device enabling implementation
of the process according to the invention, given as a non-limiting
example and detailed as follows.
The raw water, still called water to be treated, is carried by
piping 1, to which an air injection piping 2 is connected. An
automatic valve 3 regulates the flow of the latter; the water is
immediately mixed thoroughly with the introduced air, passing into
an aeration chamber or mixer 4, and then penetrates into a
biofilter reactor 5, filled with a specific filtering material 6,
called a filter bed, resting on a flooring 50 provided with a
plurality of nozzles 51. The filter bed can be constituted of
siliceous sand of effective size between 1 and 3 millimetres, or of
porous material designed specially for biofiltration, of the type
on sale under the brand name "Biolite". After treatment, the
effluent exits from the biofilter 5 through the piping 7 for
treated water, connected below the flooring 50. On the raw water
piping 1, downstream from the mixer 4, a sensor-analyser assembly 8
constitutes a first measurement means of the pH of the aerated
water, whereas an analogous apparatus 9 constitutes a second means
for measuring the oxidation-reduction potential (Eh) of the aerated
water. The signals representing the results of the two analyses are
transmitted to a computer 10 which checks that the value of the Eh
potential is really between a minimum (lower limit) and a maximum
(upper limit) determined in function of the pH value of raw water.
If this is not the case, the computer 10 sends a signal to a
regulator 11 which provides the order to increase or reduce the air
flow delivered by the valve 3 depending on whether the value of the
Eh potential of the aerated water is below the lower limit or above
the upper limit respectively.
Thus, as described above, the specific filtering material is
constituted either of sand, or of a "Biolite" type material of
effective size higher than the order of 1 to 3 mm, such as for
example 1.25 mm, that is greater by 50% than the effective size of
0.95 to 0.75 mm of the same filters used under conditions not
corresponding to iron removal and manganese removal conditions. In
the same way, the nozzles 51 of the flooring of the biofilter
reactors can comprise wider slits of the order of 0.7 to 1.2 mm
whereas formerly, the slits had a size of 0.4 mm. The filtration
speed is of the order of 30 to 50 m/sec.
Finally, the oxygenation created by the regulation will generate
the development of bacteria within the filter, these bacteria being
ferro-bacteria or mangano-bacteria according to the specific
aeration conditions created upstream of the filter. The effective
size of the filtering bed and the nozzle slits makes it possible,
taking into account the lower size of the bacteria, to avoid
obstruction of the filtering bed and the nozzles and above all to
wash the raw water filter bed, when the passage speed of water in
the filter exceeds the filtration speed.
A precision adjustment, complementary to the main adjustment of the
process described above, is ensured by control units located
downstream from the biofilter 5. The exit 7 for filtered water is
provided with a measurement means 12 for residual dissolved oxygen
and a second measurement means 13 for the pH. The signals
representative of the measurements are sent to a calculation unit
or a computer 14 which verifies that the signal representative of
the content of dissolved oxygen, for the pH values measured, is
neither below a given lower threshold, for the pH value measured,
due to consumption of part of the oxygen introduced ahead during
iron oxidation, nor above a given upper threshold, resulting from a
possible lack of precision of the regulation of air flow resulting
from the Eh potential measurement of aerated water. To begin with,
overrunning one of these thresholds detected by the computer 14 can
set off an alarm 15 which will alert the operator to verify the
upstream regulation (through the Eh potential value of aerated
water) and if necessary to adjust the values of orders sent to the
computer. After this, if optimisation of upstream regulation of the
biofilter is impossible, this will be replaced by a downstream
regulation through dissolved oxygen, carried out by a signal
emitted by the computer 14 to a regulator 16 which sends, depending
on the case, a signal to open or close the air entry valve 3 to
return within the set limits.
Furthermore, it must be remembered that the iron oxidation and
precipitation reactions freeing protons H.sup.+, are acidifying. If
the buffering capacity of the raw water is low, corresponding to
low alkalinity, during the process the pH risks undergoing a drop
incompatible with good treatment yield. The device according the
invention comprises a pH regulation station making it possible to
avoid this drop in pH. In order to eliminate this disadvantage, the
process according to the invention envisages sending the result of
the pH measurement provided by the second measurement means 13 to a
regulation unit 17 which starts, if the pH descends below a certain
set point (lower threshold), the progressive operation of an
electro-valve or a feed pump 18 which introduces into the piping 1
an alkaline solution 19 contained in a preparation tank or
reservoir 20, without the water pH going beyond the upper set limit
(upper threshold), compared with the pH measurement provided by the
measurement means 8 or the measurement means 13. The lower and
upper pH thresholds are decided in function of the nature of the
bacteria used, each bacterium having a preferential pH range.
The lower and upper limits attributed respectively to the
oxidation-reduction potential Eh of the aerated water and to the
concentration in dissolved oxygen of the treated water are deduced
by simple algorithms whose independent variable is the pH of the
corresponding water and which are stored in the memory of the
computer ad hoc.
The algorithms used correspond to: the upper and lower limits of
the Eh oxidation-reduction potential of the aerated water,
characterised by an equation of the form
expression in which the coefficients .alpha., .beta., .gamma., and
.delta. are determined case by case for each type of water.
In order to evaluate the treatment efficiency, the piping 7 for
treated water, downstream from the biofilter 5, can be provided
with a sensor-analyser unit 21 measuring the oxidation-reduction
potential Eh of the treated water and a sensor-analyser assembly 22
measuring its residual iron content. These assemblies are connected
to a computer 23 which can set off an alarm 24 if there is an
anomaly. This embodiment is given as a non-limiting example. The
different computers, 10, 14, 23, mentioned above can form a single
component capable of integrating the different signals emitted by
the sensors 8, 9, 12, 13, 21, 22, and able to command a single air
flow regulator. This component can also comprise the pH regulator
17.
In the above, the application of the invention as described in FIG.
1 referred first and foremost to a biological iron removal
treatment. The invention can regulate any other biological
treatment based on oxidation by air, in particular biological
manganese removal. The algorithms are then less complex, since it
is sufficient to ensure that the fundamental physico-chemical
parameters of the process (potential, dissolved oxygen, possibly
rH) are all well located above a certain set point, without it
being necessary to take into consideration an upper limiting value,
whatever the parameter under consideration.
In the same way, in another variant shown in FIG. 2, it is possible
to put a device for iron removal according to the invention in
series with a downstream device for manganese removal. The exit 7
from the ferro-bacteria biofilter reactor 5 is linked directly or
indirectly to the entrance to a second aeration chamber 4' into
which the treated water from the ferro-bacteria biofilter reactor
arrives together with the air 2 injected by a second valve 3'. The
water is then treated by percolation through a second biofilter
reactor 5' provided with an exit 7' and comprising a porous
mangano-bacteria supporting bed 6'. Third measurement means 9' of
Eh oxidation-reduction potential or dissolved oxygen and
measurement means 8' of pH are set at the exit from the second
aeration chamber. The representative measurement signals are sent
to a computer 10' which compares the representative signal of the
potential measured with a lower limit given as a function of the
representative signal of the pH measurement. If the measured
potential is lower than the lower limit, the computer 10' delivers
a command signal to a regulation means 11' acting on the second
valve 3' to enable adjustment of the air flow. It is to be noted
that the computer 10' can use the pH measurement of the water
treated by the iron removal device, made by the sensor 8 or the
second measurement means 13 described above. The water exiting from
the ferro-bacteria biofilter reactor can if necessary undergo
special treatments before being treated by the manganese removal
device.
The invention has been applied as a pilot station to the treatment
and elimination of iron and manganese in ground water. The
installation comprises two filtration steps operating according to
the process according to the invention, one adjusted for iron
removal and the second adjusted for manganese removal. The results
are given in the table below, and demonstrate the low concentration
of iron and manganese in water treated by the process according to
the invention.
PARAMETERS RAW WATER TREATED WATER pH 7.0 7.8 Fe (mg/l) 13 <0.1
Mn (mg/l) 2 <0.04
FIG. 3 shows the evolution of the concentration in ferrous iron
(CFe.sup.2+) of water treated in different plants as a function of
time (Tps) of treatment in hours. The curves (.quadrature.,
.largecircle., .DELTA.) represent the results obtained on an
existing iron removal plant, operating entirely on the
physico-chemical principle of chlorine oxidation, followed by
filtration over manganese greensand. The curves (.quadrature.,
.quadrature., .quadrature.) showing the results obtained on a pilot
plant for biological iron removal, functioning according to the
invention, were tested in parallel. The results, shown for three
filtration cycles speak for themselves and emphasise all the
interest of this type of biological treatment which demonstrates a
consistent low residual concentration of iron whereas for the
existing physico-chemical process, this rises with the hours of
utilisation of the plant.
Also, the process according to the invention, on a biological
manganese removal filter, was tested on a plant operating at a
filtration speed of 30 m/hr and the table below summarises the
excellent results obtained.
PARAMETERS RAW WATER TREATED WATER pH 7.65 7.65 Mn (mg/l) 0.7
<0.02
Other modifications known to those skilled in the art are also
within the scope of the invention.
* * * * *
References